In fluid or gas handling systems in industry, particularly pressurized systems, it is known to provide a so-called closure assembly to provide quick and safe access into some part of the interior of the fluid or gas handling system. For example, in the gas and/or chemical industries, it is common for there to be various pipelines arid vessels that generally operate in a pressurized environment. When the systems are not in operation, it is often desirable to have access to the inside of the systems for cleaning, inspection, and/or the changing of filters or other replaceable elements which may be present.
Some applications of closure systems include those in the petrochemical, pharmaceutical and chemical process industries such as blow downs, manways, meter provers, filters, strainers, coalescers, waste disposal vessels, and autoclaves. Typical closures may for example range in diameter from 4 inches to 24 inches, with working pressures up to ANSI 300 (740 psi/51.1 bar) and temperatures from −50 degrees F. to 400 degrees F.
One approach to providing a closure is to provide a flange around an opening at the end of a hub-shaped extension that extends from some part of the fluid handling system. A covering or closing element, which forms a cap often referred to as a head, and which may simply be a disk shape or a dome-shaped piece of material, is removably but securely attached over the flanged opening to provide a fluid-tight and pressure-tight seal when closed. The cover is removable to provide access to the interior of the pressurized system via the opening in the flange.
One way of securing the cover element, or closure, onto the flanged opening has been simply to provide a series of corresponding bolt holes through the cover and around the circumference of the flange so that individual bolts may be inserted through the corresponding holes and tightened. Tightening the bolts presses the circumference of the closure against the flange, and a sealing element such as a gasket may be provided between the closure and the flange. Tightening all the bolts provides closing pressure and a seal at the gasket to resist escaping of the fluid or gas daring system operation. A disadvantage of these bolt type closures is that individually installing and/or removing bolts can be time consuming and cumbersome, particularly where a large number of bolts are required.
Another type of closure is the so-called screw type of closure, in which the flange has a threaded outer surface, and the closing element is shaped like a cap and has a corresponding threaded inner surface. This closure is screwed onto the flange to provide a seal. A disadvantage of screw type closures is that closing the cap usually requires that the cap be rotated many degrees, even several rotations.
A third type of closure is the so-called rotary lug type closure. In this arrangement, the outer circumference of the flange has several lugs projecting outwardly, and the cover or head has grooves and corresponding lugs projecting inwardly. Thus, the head can be oriented at an angle where it can be pushed axially onto the flange. The head can be rotated a specified number of degrees so that the lugs interfere with each other and prevent the head from moving axially. In this arrangement, once the head has been rotated so that the lugs are fully interfering, the head is held pressure-tight against the flange, to resist leakage and pressure.
Lug type rotary systems can be preferable to screw type systems because the cover can be moved from a fully openable to a fully closed position merely by rotating the cover by a partial turn, e.g., by 45 degrees. This can be a more simple operation than the many rotations sometimes required on a screw type closure.
Industrial systems often handle fluids and/or gases at very high pressures. Before accessing these systems via a closure, it is generally known to depressurize the system by means of a main bleed valve located somewhere in the system. It is be desirable to have a safety device to prevent opening of these closures where significant pressure exists inside the system, for example as would occur if the main bleed valve operation has not been performed.
Since these systems sometimes have residual pressures even after the main bleed process has been performed, it can also be desirable for the closure to have some type of safety device to prevent opening of the closure even when a residual internal pressure is present. It may sometimes also desirable to have some arrangement for bleeding out these residual pressures at the location of the closure, so that pressure at the closure can first be bled out, and then opening of the closure can be effected, all at the location of the closure. Thus, there is a need for a system and method that (1) provides a warning to the operator of full and/or residual pressure and/or (2) releases pressure in the region of closure, before the closure can be opened.